As reduction in size of a quartz crystal resonator unit has been demanded in recent years, it is necessary to reduce the size of a quartz crystal blank. However, when the size of a quartz crystal blank is reduced, the influence of a sub-vibration becomes pronounced or an influence of vibration leakage arises, and therefore series resistance tends to increase. Examples of existing inventions related to a quartz crystal blank and aimed at reduction of series resistance include a quartz crystal resonator plate described in Patent Document 1. End portions of the quartz crystal resonator plate are chamfered (beveled). Thus, vibration energy is confined under excitation electrodes, and appropriate series resistance can be achieved.
As described above, regarding a quartz crystal blank, various improvements have been made in order to achieve appropriate series resistance.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2013-34176